Encyclopedia of Health and Medicine

226 The Urinary System
typically 7 to 10 days. It is important to continue
taking all prescribed doses of the antibiotic, even
when symptoms improve, to make sure the
antibiotic kills all the bacteria. The doctor may
prescribe low-DOSE antibiotic medications for longterm
preventive therapy (six months to a year) in
women who have recurrent UTIs.
The medication phenazopyridine, a topical
anesthetic that numbs the inner lining of the bladder
and urethra, relieves discomfort during the
first 36 to 48 hours of the UTI until the antibiotic
begins eliminating bacteria. Phenazopyridine colors
the urine deep orange and stains clothing.
Some people experience intense bladder spasms,
for which the doctor may prescribe a short course
of antispasmodic medications such as flavoxate or
methenamine.
ANTIBIOTICS COMMONLY PRESCRIBED TO TREAT UTI
amoxicillin cefaclor cefixime
cefotaxime cefpodoxime cefprozil
cefuroxime axetil ciprofloxacin doxycycline
fosfomycin levofloxacin nitrofurantoin
norfloxacin ofloxacin sparfloxacin
sulfamethoxazole tetracycline TMP-SMX
trimethoprim
Risk Factors and Preventive Measures
UTIs are common in girls and women though
uncommon in boys and men because of differences
in anatomy. The very short female urethra
provides an easy route for bacteria to travel into
the bladder. Health experts estimate that one in
five women will have at least one UTI during her
lifetime. Measures to reduce the risk for UTI
include
• drinking enough water (six to eight 8-ounce
glasses daily)
• urinating when the bladder signals it is full
• wiping with toilet tissue from front to back
• urinating soon after SEXUAL INTERCOURSE
• prophylactic antibiotics when UTI occurs three
times in a year or more frequently
About 20 percent of women who have one UTI
have another; recurrent UTI is rare in men.
Though untreated or undertreated UTI can cause
serious and permanent damage to the urinary system,
people who have appropriately treated UTIs
typically recover completely and without residual
complications.
See also CYSTITIS; GLOMERULUS; NEPHRON; SEXUALLY
TRANSMITTED DISEASES (STDS); URETHRITIS.
urination The act of passing URINE from the BLAD-
DER, also called uresis or micturition. Urination
occurs when the urethral sphincter relaxes at the
same time the detrusor MUSCLE that forms the middle
layer of the bladder wall contracts, squeezing
urine into the URETHRA. The urethra carries the
urine to the meatus, its opening on the outer surface
of the body. In men the meatus is at the tip of
the PENIS; in women the meatus is within the VULVA
between the CLITORIS and the VAGINA. Urination ends
when the bladder sphincter closes and the residual
urine in the urethra passes from the body.
Urination is a blend of involuntary and voluntary
control. At birth urination is completely
under the control of the micturition REFLEX and
the sympathetic NERVOUS SYSTEM, which regulates
involuntary functions. The micturition reflex is
the series of events that begins when the filling of
the bladder with urine activates specialized nerves
in the bladder wall called stretch receptors. The
stretch receptors send NERVE signals out to the
SPINAL NERVES (S2, S3, and S4) that control the urethral
sphincter and the detrusor muscle. The
spinal nerves send back the nerve signals that
stimulate the detrusor muscle to contract and the
urethral sphincter to relax. A structure within the
pons of the brainstem, the pontine micturition
center (PMC), coordinates these functions to
occur simultaneously.
The ability to control urination becomes possible
around the ages of three to five when the
muscles and nerve paths mature. At this point of
development the BRAIN can override the involuntary
nerve processes and the pubococcygeal muscle,
which is a voluntary muscle, can override the
involuntary muscle functions of the bladder. The
normal frequency of urination varies among individuals
and with fluid consumption, which largely
determines urine volume. A healthy adult produces
between 1.5 and 3 liters of urine every 24
hours. Typically the stretch receptors respond
when the bladder contains about 200 to 300 milli-